Friction stir welding method, and method for manufacturing car body

ABSTRACT

A cutting tool  60  cuts along the butted portion between two members  10, 20 . A filling material  30  is inserted to the gap  40  formed by said cutting, and a roller  70  presses protrusions  12  and  22  to crimp said protrusions  12  and  22  so as to fix said filling material to position. Next, friction stir welding is performed to the protrusions  12, 22  and the filling material  30  using a rotary tool  80 . In another example, instead of cutting, the filling material can be welded and filled to the gap. In yet another example, cutting can be performed so as to approximate the two members before performing the friction stir welding step.

FIELD OF THE INVENTION

[0001] The present invention relates to a friction stir welding method.Especially, it relates to a welding method appropriate for manufacturingthe body of a car that runs on rails, such as a railway car.

DESCRIPTION OF THE RELATED ART

[0002] Friction stir welding method is a method for bonding members byinserting a round shaft (called a rotary tool) to a joint portion andmoving the tool along the joint line while rotating the tool, so as toheat, soften and plasticize the joint portion thereby performingsolid-phase bonding of the members. The rotary tool comprises alarge-diameter portion and a small-diameter portion. The small-diameterportion is inserted to the members to be bonded, and the end surface ofthe large-diameter portion comes into contact with the members. Thesmall-diameter portion is provided with a screw. Moreover, a protrusionis formed to the butted portion of the two members to be bondedtogether, and the rotary tool is inserted from the side provided withthis protrusion so that the metal constituting the protrusion fills thegap between the two members. The large-diameter portion of the rotarytool is inserted to the protrusion. When friction stir welding hollowmembers, the connecting plate that connects two face plates is used asthe supporting board when friction stir welding the hollow memberstogether. These methods are disclosed for example in Japanese PatentPublication No.3070735 (U.S. Pat. No. 6050474) and Japanese PatentLaid-Open Publication No. 2000-334581 (EP1055478A1).

[0003] Moreover, Japanese Patent Laid-Open Publication No. 2000-233285discloses in FIG. 14 a method for friction stir welding two memberswhile positioning a filling member in the gap formed between the twomembers. Furthermore, Japanese Patent Laid-Open Publication No.2000-167677 (EP0992314A2) discloses a friction stir welding method forwelding a first member having a protrusion with a second member nothaving a protrusion, wherein intermittent buildup welding is performedto the second member before performing the friction stir welding.

SUMMARY OF THE INVENTION

[0004] When a gap exists between the two members to be welded, it isvery difficult to perform friction stir welding. Therefore, a protrusionis formed to the surface of the member where the rotary tool is to beinserted, so as to fill the gap with the metal constituting theprotrusion. However, in reality when the gap exceeds 1 mm for example,it is difficult to obtain a good joint. It may be possible to increasethe diameter of the rotary tool as the gap widens, but this may causeother inconveniences.

[0005] The car body of a railway car and the like that runs on railsinclude side structures that constitute the inner side surfaces of thevehicle, a roof structure, and an underframe that forms the floor. Thefirst step for manufacturing a car body is to manufacture the sidestructures, the roof structure, and the underframe, respectively, bybonding plural extruded members. Next, these structures are bonded toform the car body. The size of each side structure, roof structure andunderframe is approximately 20 m in length and 3 m in width, so there isa possibility of a large fabrication error. This error causes the gap ofthe joint portion to easily exceed 1 mm. The object of the presentinvention therefore is to obtain a good weld even when a large gapexists.

[0006] The second object of the present invention is to provide a simplefriction stir welding method for bonding the underframe and the sidestructures of the car body, and for bonding the side structures and theroof structure thereof.

[0007] The objects mentioned above are achieved by positioning a memberfor filling the gap to the gap existing in the butted portion betweentwo members, and then performing friction stir welding thereto.

[0008] Moreover, the member for filling the gap can be arranged in a gapformed by cutting the butted portion of the two members.

[0009] Even further, the butted portion of the two members can be cutand the two members can be moved closer together before performingfriction stir welding thereto.

[0010] As for the second object of providing a simple friction stirwelding method for welding the underframe and the side structures,either the surface plate of the underframe is used as supporting means,or a supporting device is arranged between two side structures, therebyfacilitating the process.

[0011] The friction stir welding of the side structures and the roofstructure is facilitated by providing a support device between the twoside structures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 shows the steps for welding two members according to oneembodiment of the present invention;

[0013]FIG. 2 is a cross-sectional view taken at line II-II of FIG. 1;

[0014]FIG. 3 is a cross-sectional view taken at line III-III of FIG. 1;

[0015]FIG. 4 is a cross-sectional view taken at line IV-IV of FIG. 1;

[0016]FIG. 5 is a view of the welding device according to anotherembodiment of the present invention;

[0017]FIG. 6 is a front view of the welding device according to anotherembodiment of the present invention;

[0018]FIG. 7 is a cross-sectional view taken at line VII-VII of FIG. 6;

[0019]FIG. 8 is a cross-sectional view taken at line VIII-VIII of FIG.7;

[0020]FIG. 9 is a vertical cross-sectional view showing the jointportion between the underframe and the side structure of FIG. 6;

[0021]FIG. 10 is a drawing corresponding to FIG. 9 according to anotherembodiment of the present invention;

[0022]FIG. 11 is a drawing corresponding to FIG. 9 according to yetanother embodiment of the present invention;

[0023]FIG. 12 is a front view showing the welding device according toanother embodiment of the present invention;

[0024]FIG. 13 is a vertical cross-sectional view showing the jointportion between the side structure and the roof structure of FIG. 12;

[0025]FIG. 14 is a front view showing the joint portion according toanother embodiment of the present invention; and

[0026]FIG. 15 is a view showing the welding steps according to anotherembodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0027] First, the basic embodiment of the present invention will beexplained with reference to FIGS. 1 through 4. FIG. 1 shows the weldingoperation in steps performed in order from (A) to (D).

[0028] In FIG. 1 (A), two plate-shaped members 10 and 20 are mounted ona base 50 and butted to each other. The two members 10 and 20 are buttedso as to minimize the gap between them. The member 10 comprises aprotruding block 15 along the butted portion against the member 20, andthe member 20 rests on the block 15. Protrusions 12 and 22 are formedrespectively on the upper surfaces of the butted portion of members 10and 20. At this state, the members 10 and 20 are fixed to the base 50using a binding equipment (not shown). The members 10 and 20 are made ofaluminum alloy. The butted portion will hereinafter be called the jointline.

[0029] After the members are bound as above, the butted surface of thetwo members 10 and 20 are cut from above using a cutting tool 60. Thisforms a gap (groove) 40 having a constant width to the butted surfaces.The width of the cut (gap, groove) 40 is greater than the gap thatexisted when the members 10 and 20 were butted. The bottom surface ofthe gap 40 (the bottom of the cut) does not go below the upper surfaceof the protruding block 15. (FIG. 1 (A))

[0030] A sensor is used to detect the width of the two protrusions 12and 22, and the center of the cutting tool 60 is placed to the center ofthe detected width, thereby performing the cutting process. Theinsertion depth of the cutting tool 60 is controlled to a fixed depth bydetecting the position of the upper surface of the protrusions 12 and22. The cutting is performed as dry cutting. The swarf is either blownaway by compressed air or aspirated by a dust collector. The cuttingtool 60 shown in FIG. 1 is an end mill, but a circular saw can be usedinstead.

[0031] Next, a filling material 30 is arranged in the gap 40 formed bythe cutting process. The height of the filling material 30 is set sothat the upper surface of the material 30 is positioned below the uppersurface of the protrusions 12 and 22. The upper surface of the fillingmaterial 30 is positioned above the line extended from the upper surfaceof the plates 11 and 21 of members 10 and 20 excluding the protrusions12 and 22. The width of the filling material 30 should preferably be asclose to the width of the gap 40 as possible, but still easy to insertto the gap. The difference in the width of the gap 40 and the width ofthe filling material 30 is less than 1 mm. (FIG. 1(B), FIG. 2)

[0032] Next, the upper surfaces of the protrusions 12 and 22 close tothe gap 40 are pressed from above, and the corners of the protrusions 12and 22 are bent toward the gap 40. Thereby, the filling material 30 ispressed downward, and fixed to the members 10 and 20. The fixationprevents the filling material 30 from moving when the rotary tool 80performs the friction stir welding.

[0033] This crimping process is performed by running a roller 70 alongthe gap 40. The tip of the roller is formed into a trapezoid shape. Thecenter of width of the roller 70 is positioned to the center between thetwo members 10 and 20 (center of the gap 40). The sloped surfaces of theroller 70 presses the corner of the protrusions 12 and 22. Thereby, thecorners of protrusions 12 and 22 are crimped. A sensor detects the widthof the two protrusions 12 and 22, and the center of the roller 70 ispositioned to the center thereof, and the roller is pressed. (FIG. 1(B),FIG. 3)

[0034] The roller 70 presses the protrusions 12 and 22 toward the groove40 with predetermined power provided by an air cylinder 75. The aircylinder 75 can expand and contract freely so as to correspond to theheight variation of the protrusions 12 and 22. If beads from a tack weldexplained in the following exist, the roller 70 can run over them.

[0035] Next, a rotary tool 80 is inserted to the butted portion fromabove, thereby friction stir welding the three members together, whichare the members 10 and 20 and the filling material 30. The rotary tool80 moves along the joint line. The tip of the small-diameter portion 82of the rotary tool 80 reaches the protruding block 15. The diameter ofthe small-diameter portion 82 is greater than the width of the gap 40. Asensor detects the width of the two protrusions 12 and 22, and thecenter of the rotary tool 80 is positioned at the center thereof whenperforming the friction stir welding. The insertion depth of the rotarytool 80 is controlled to a fixed depth by detecting the upper surfaceposition of the protrusions 12 and 22. (FIG. 1(C) and (D), FIG. 4)

[0036] If necessary, after friction stir welding, the joint portion andthe protrusions 12 and 22 protruding from the upper surface of theplates 11 and 12 are cut off, to form a smooth flat surface.

[0037] One example of the size of each member will now be explained. Thewidth of the gap 40: 3 mm; the depth of the gap 40: 6 mm; the thicknessof plates 11 and 21: 4 mm; the height of the protrusions 12 and 22(excluding the portion of plates 11 and 21): 2 mm; the width ofprotrusions 12 and 22: 8 mm; the width of the filling material 30: 2.5mm; the height of the filling material 30: 5.5 mm; the diameter of thelarge-diameter portion 81 of the rotary tool 80: 15 mm; the diameter ofthe small-diameter portion 82: 6 mm; the tilt angle of the rotary tool80: 4°. When performing friction stir welding, the boundary between thelarge-diameter portion 81 and the small-diameter portion 82 (moreprecisely, the lowest end of the large-diameter portion 81) ispositioned between the upper surface of the plates 11 and 21 and theupper surface of the filling material 30.

[0038] According to this embodiment, even if a gap exceeding 1 mm existsalong the joint line when two members are butted together, the cuttingprocess expands the gap to a predetermined size, and next the fillingmaterial 30 is positioned thereto reducing the gap to less than 1 mm,before the friction stir welding is performed. Therefore, a good weld isobtained. The gap between the filling material 30 and the gap 40corresponding to the thickness of the plates 11 and 21 is filled usingthe metal forming the protrusions 11 and 21 and the upper part of thefilling material 30 as source material.

[0039] If the filling material 30 is not sufficiently fixed topositioned by the crimping, an arc welding can be performed tointermittently tack weld the filling material 30 to the protrusions 11and 21.

[0040] Next, the embodiment of FIG. 5 will be explained. Reference 61 isa circular saw used as the cutting tool 60. Behind the circular saw 61is a suction opening 65 that aspirates the swarf. Further, a rubberplate 66 prevents the swarf from moving downstream. The filling material30 is spooled around a drum 90. The filling material from the drum 90 issmoothly bent into an arc-shape by guide rollers 93 b, 93 c and 93 d,and travels through a cylindrical guide 95 before being inserted to thegap 40. Such rollers 93 b, 93 c and 93 d and the guide 95 areappropriately positioned between the drum 90 and the roller. When thefilling material 30 is positioned in the gap 40, it is fixed thereto bythe roller 70, and friction stir welding is performed by the rotary tool80. These devices are mounted on a single track. As the track moves, thedrum 90 reels off the filling material 30.

[0041] Upon crimping the protrusions 12 and 22 to fix the fillingmaterial 30, it is preferable to first weld the end portion of thefilling material 30 to the protrusions 12 and 22.

[0042] According to this embodiment, the roller 70 inserts the fillingmaterial 30 into the gap 40 is also the roller 70 that crimps theprotrusions 12 and 22, but independent rollers can be used for the twopurposes. The roller that inserts the filling material 30 to the gap 40presses the upper surfaces of the filling material 30.

[0043] Further, the roller 70 is used to crimp the protrusions 12 and 22to fix the filling material 30, but instead, the upper surface of thefilling material 30 can be pressed and fixed by the roller 70. Further,the upper surface of the filling material 30 can protrude above theupper surface of the protrusions 12 and 22. It is preferable to mountplural rollers 70 along the direction that the track runs, so as to fixthe material securely.

[0044] According further to the present embodiment, the roller 70 isused to press the protrusions 12 and 22, but instead, the twoprotrusions 12 and 22 can be hammered intermittently. The hammeringmember should have a small cross-sectional area, such as a chisel.Moreover, the swarf generated when cutting the groove 40 can be removedby blowing compressed air thereto.

[0045] If hairline finishing is to be performed to the surface after thefriction stir welding is performed and the surface is smoothed out, thefilling material 30 should be the same material forming the base members10 and 20. If a filling material that is different from the material ofthe base members is used, and hairline finishing is performed withoutpainting the welded portion, the joint portion can be discolored, andthe appearance is deteriorated. However, if the filling materialutilizes the same material as the base members, less discolorationoccurs, and the appearance is improved.

[0046] Next, another embodiment will be explained with reference toFIGS. 6 through 9. This embodiment applies the present method tomanufacture the car body of a vehicle that runs on rails, such as arailway car. The car body of the railway car comprises for example anunderframe 110 constituting the floor of the car, the side structures120, 120 constituting the side surfaces thereof, and a roof structure130 constituting the roof of the car. First, the roof structure 130 ismounted on the upper portion of one pair of side structures 120, 120,and then they are welded and integrated. Then, the body is mounted onthe underframe, which are then welded together. The following is anexplanation of a friction stir welding device that welds the underframeto the side structures.

[0047] The underframe 110 is mounted on and fixed to a base 210. Theside structures 120, 120 are mounted on the underframe 120. A roofstructure 130 is welded onto the upper area of the side structures 120,120. After welding the side structures 120, 120 and the roof structure130, the welded body is mounted on the underframe 120.

[0048] The upper areas of the side structures 120, 120 are supported bya supporting device 230. The supporting device 230 is mounted on a frame220 positioned along both side surfaces of the car body. The supportingdevice 230 can expand and contract in the horizontal direction. Asupporting device 240 is arranged to the inner side of the car body forsetting the interval between the pair of side structures 120 and 120 toa predetermined size and for setting the vertical degree of thestructures 120, 120. The supporting device 240 is positioned between theupper portions of the side structures 120, 120, the lower portionsthereof, and between the upper portion and the lower portion thereof.The supporting device 240 can be support bars for increasing theinterval between the side structures 120 and 120, or chains for reducingthe interval thereof. Each are equipped with a turnbuckle, enabling tovary the interval. The chain should be hooked on a window and the liketo pull the structure. Further, the lower end of the side structures 120are pressed from the exterior of the vehicle body toward the innerdirection.

[0049] Welding devices 300, 300 are positioned next to both sidesurfaces of the car body. The upper and lower ends of each weldingdevice 300 is supported by rails 301, 302 which run linearly along thecar body. The welding device 300 is positioned on a track 310. Thewelding device 300 is mounted to the lower rail 301 via a roller, and isfurther equipped with a roller that contacts the left and right sides ofthe rail. The upper area of the welding device 300 is equipped with aroller that contacts the left and right sides of the rail. The rail 302is formed on the upper portion of the frame 220.

[0050] The welding device 300 is the equipment disclosed in the previousembodiment. The welding device 300 is placed on an elevating platform320 of the track 310. The elevating platform 320 moves up and downguided by the poles on the left and right sides of the square frame ofthe track 310. A seat 330 that rotates in the vertical direction ispositioned at the upper area of the elevating platform 320. On the uppersurface of the rotary seat 330 is a seat 340 that moves in thehorizontal direction. On the upper surface of the moving seat 340 isplaced a seat 350 that moves up and down. The equipment disclosed in theprevious embodiment is mounted on these up/down seats 350, 350. That is,on one seat 350 is mounted the circular saw 61, the driving devicethereof, the suction opening 65, the plate 66, the sensor and the like.On the other seat 350 is mounted the rollers 70, 93 b, 93 c, 93 d, theguide 95, the rotary tool 80, the driving device thereof, the sensor andthe like. On the upper portion of the track 310 is positioned the drum90.

[0051] Each of the above-mentioned sensors detect the width and theposition of the protrusions, based on which the horizontal movement seat340 and the up/down seat 350 are moved in order to control the positionand the depth of the circular saw 61 and the rotary tool 80. Thehorizontal movement seat 340 changes the distance from the car body.

[0052] The rotary seat 330 is used when the shape of the portion of thecar vehicle to be welded is tilted from the vertical surface.

[0053] In FIG. 9, the underframe 110 and the side structure 120 are eachformed by welding plural hollow members. Each of the surface plates 121b and 121 c of the hollow member 121 at the lower end of the sidestructure 120 are butted to the hollow member 111 at the end of theunderframe 110. The hollow member 111 is called a side beam, and theheight or the thickness of the plate is greater than the other hollowmembers 112.

[0054] The surface plate 121 c facing the interior of the car is mountedon the upper surface plate 111 b of the hollow member 111. They aresubstantially orthogonal. This butted portion is fillet-welded by arcwelding from the interior side of the car body.

[0055] The surface plate 121 b facing the exterior is butted to therecessed portion 111 d formed to the upper area of the hollow member111, and is mounted on the recessed portion 111 d. This butted portionis friction stir welded from the exterior side of the car body.

[0056] The recessed portion 111 d exists on the hollow member 111between the upper surface plate 111 b and the perpendicular plate 111 cfacing the exterior side. The recessed portion hid is opened both to theupper direction and to the outer direction. The recessed portion 111 dis provided with a protruding block 111 f protruding upward. Theprotruding block 111 f adjoins the back side of the surface plate 121 b.

[0057] The center of thickness of the circular saw 61, that is, theextension of axial center of the rotary tool 80, is within the range ofthe thickness of the surface plate 111 b. This enables the load whenperforming the friction stir welding to be supported by the surfaceplate 111 b, thereby preventing the deformation of the joint portion,and enabling a good weld.

[0058] The upper surface plates 111 b and 112 b of the hollow member 111and 112 of the underframe 110 are substantially positioned on the sameplane. The exterior side of the lower end of the surface plate 121 b andthe exterior side of the upper end of the connecting plate 111 c areeach provided with protrusions 12, 22, respectively.

[0059] The structure of the joint portion between the left sidestructure 120 and the underframe 110 is identical to that explainedabove.

[0060] The welding steps will now be explained. The underframe 110 ismounted on the base 210, and side structures 120, 120 are mounted ontop, with supporting devices 230 and 240 fixing the side structures tothe predetermined position. Then, the underframe 110 and the sidestructures 120, 120 are tack-welded intermittently both from theinterior and exterior of the car. Next, the surface plates 121 b and 111b are arc-welded from the interior side of the car.

[0061] Next, the left and right welding devices 300, 300 are driven insynchronism, and welding is performed in synchronism. The circular saw61 of the welding device 300 forms a groove 40 to the joint portion intowhich is positioned the filling material 30, before performing thefriction stir welding.

[0062] The cutting of the groove (gap) 40 is started from thelongitudinal end portion of the car body using the circular saw 61.After forming a groove 40 of predetermined length, the movement of thetrack 310 is stopped, and filling material 30 is reeled off from thedrum 90 and inserted to the groove 40.

[0063] Next, the filling material 30 inserted to the groove 40 istack-welded to the protrusions 12 and 22. The welding position is at thestarting end of the filling material 30 inserted to the groove 40. Next,the roller 70 is protruded toward the groove 40 at a predeterminedposition, and the movement of the track is started. The cutting is alsoresumed. At the same time the inserting of the filling material 30 tothe groove 40 is started, the roller 70 starts to fix the material 30 toposition.

[0064] When the rotary tool 80 of the friction stir welding device movesto the position where the joint line starts, the movement of the track310 is stopped. While rotating the rotary tool 80, the tool 80 isinserted to the portion to be welded. Next, the movement of the track310 is resumed.

[0065] The welding devices 300 and 300 on the left and right sides ofthe car body are moved in synchronism when performing the friction stirwelding. In other words, on the line extending from the axial center ofthe rotary tool 80 of the right welding device 300 is substantiallypositioned the axial center of the rotary tool 80 of the left weldingdevice. Between the left and right devices are surface plates 111 b and112 b of the underframe 110. Therefore, the large load while performingthe friction stir welding is supported by the surface plates, whichprevent the underframe from deforming.

[0066] However, in general, the axial center of the rotary tool 80 istilted toward the direction in which it moves. Therefore, the rotarytool 80 will not be positioned on the line extended from the axialcenter of the other tool 80. In this case, the other rotary tool 80cannot support the load of one rotary tool 80, but it can support thearea surrounding it. Therefore, the friction stir bonding is performedwithout the underframe being deformed.

[0067] In order to support the load of one rotary tool 80 from the otherside, a roller is used to support the area extended from the axialcenter of one rotary tool 80, which is moved in synchronism with saidone rotary tool 80. When a plural number of rollers is used, the rollersare positioned along the joint line. Further, a supporting device forsupporting the area surrounding the other joint portion is provided. Onthis other side, the supporting device can be provided without therotary tool 80. In this case, the support device supports either thejoint portion or a non-joint portion.

[0068] It is common to provide a camber to the car body. When a camberis formed to the underframe 110, the height of the cutting process andthe height of the friction stir welding process is moved up and downaccording to the camber. In this case, it is preferable to use an endmill instead of the circular saw.

[0069] According to the embodiment above, normally the filling materialis fixed to position by crimping the protrusions 12 and 22, but it canalso be fixed by welding predetermined intervals thereof. The weldingposition is set between the circular saw 61 and the guide 95.

[0070] The welding of the surface plate 121 b of the hollow member 121and the surface plate 111 c of the hollow member 111 is performed at theconnecting portion 111 h provided between the surface plate 111 c andthe connecting plate 111 g that connects the substantially parallel twosurface plates (one is 111 c). The surface plate 111 c above theconnecting portion 111 h is recessed so that the surface plate 121 b canfit thereto. Thereby, the lower end of the surface plate 121 b is buttedto the surface plate 111 c positioned below the connecting portion 111h. The connecting plate 111 c is positioned along the line extended fromthe axial center of the rotary tool 80. This supports the load of therotary tool. The end portion of the surface plate 121 c is welded ontothe surface plate 111 b.

[0071] The embodiment of FIG. 10 will be explained. On the external sideof the hollow member 111 at the end of the underframe 110 is a block(corresponding to the surface plate) 111 j protruding upward. This isbutted against the external-side surface plate 121 b of the hollowmember 121 of the side structure. On the back side of the butted portionof the block 111 j and the surface plate 121 b is positioned theconnecting plate 121 d that connects the inner and outer surface plates121 b and 121 c. The connecting plate 121 d is substantially orthogonalto the surface plates 121 b and 121 c. Therefore, the connecting plate121 d is positioned along the line extending from the axial center ofthe rotary tool 80 during welding. At the joint portion between theconnecting block 121 d and the surface plate 121 b exists the recessedportion and the protruded block to which the surface plate 121 b fits,similar to the former embodiment.

[0072] After welding the surface plate 121 c and the surface plate 111 btogether, the supporting device 250 is positioned so as to contact thesurface plate 121 c. In the embodiment, plural supporting devices 250are positioned along the longitudinal direction of the car body. Thesupporting device can expand and contract freely. Next, friction stirwelding is performed. The load on one rotary tool 80 is transmitted tothe side of the other rotary tool 80 via the supporting device 250.

[0073] The embodiment of FIG. 11 will now be explained. Two protrudingblocks 111 j, 11 j are formed on top of the hollow member 111. The twoprotruding blocks (corresponding to surface plates) 111 p, 111 p areconnected by a connecting block 111 q. The connecting block 111 q ispositioned similar to the connecting block 121 d. At the connectingportion between the connecting block 111 q and the protruding blocks 111p, 111 p are provided a recessed portion and a protruding block to whichare fit the surface plates 121 b and 121 c, similar to the formerembodiment.

[0074] After welding the surface plate 121 c and the protruding block111 p, the supporting device 250 is positioned. The supporting device250 should preferably contact both the surface plate 121 c and theprotruding block 111 p. The connecting plate 111 q is positioned alongthe line extending from the axial center of the rotary tool 80 whenperforming the friction stir welding.

[0075] According to this embodiment, there is no need of a supportingdevice 250 if the protruding block 111 p is short, since the underframe110 is sufficiently strong.

[0076] The embodiment shown in FIGS. 12 and 13 is explained. Thisembodiment relates to a welding device for welding the roof structure130 and the side structure 120. The side structures 120, 120 are mountedon a base 210B, and the roof structure 130 is mounted on top. Thisassembly is supported from the interior and exterior of the car body bythe supporting device 230B and 240B. The supporting device 240B supportsthe roof structure 130 and side structures 120 by pulling or pushingfrom the interior of the car body. The supporting devices 230B and 240Bcorrespond to the supporting devices 230 and 240 of the formerembodiment. Further, the lower end of the side structure 120 is insertedto the recessed portion of the base 210B and thereby being positioned.

[0077] After fixing the side structures 120, 120 and the roof structure130 to position by the supporting device 240B, the butted portionbetween the side structures 120, 120 and the roof structure isarc-welded from the inside of the car body. After welding, a supportingdevice 250 is positioned between the left and right welded portions. Thesupporting device 250 supports the area near the welded portions. Thesupporting device 250 is a stay bar.

[0078] Next, the left and right tracks 310B, 310B are moved as mentionedabove, while the welding devices 300B, 300B cut grooves, fill thefilling material to the grooves, and perform friction stir welding. Theload added during the friction stir welding is supported by theconnecting plate 123 c and the rotary tool 80 on the other side throughthe connecting plate 123 c at the welded portion and the supportingdevice 250.

[0079] The details of the welded portion between the hollow member 126at the upper end of the side structure 120 and the hollow member 131 atthe lower end of the roof structure 130 will be explained. The hollowmember 126 (131) includes two surface plates 126 b and 126 c (131 b and131 c) and connecting plates 126 d (131 d) arranged in a trussed state.The end of the surface plate 131 b and the end of the surface plate 131c are connected by a slanted connecting plate 131 d. However, there isno connecting plate connecting the end of the surface plate 126 b andthe end of the surface plate 126 c. Therefore, the end of the surfaceplate 131 c (126 b) is protruded further toward the end portion than thesurface plate 131 b (126 c). At the connecting point (junction) betweenthe two connecting plates 131 d, 131 d and the surface plate 131 b isformed a recessed portion similar to the one mentioned in the formerembodiment, with a protruding block formed to the back surface thereof.At the connecting point (junction) between the surface plate 126 c andthe end of connecting plate 126 d is also formed a recessed portion asmentioned in the former embodiment, with a protruding block formed tothe back surface thereof. The surface plate 126 b of the hollow member126 fits to the recessed portion and the protruding block of the surfaceplate 131 b. The surface plate 131 c of the hollow member 131 fits tothe recessed portion and the protruding block of the surface plate 126c. The butted portion between the surface plates 126 b and 131 b facingthe exterior of the car is provided with protrusions 12 and 22. Thecenter of thickness of the circular saw 61 and the line extended fromthe axial center of the rotary tool 80 exists at the cross point of twoconnecting plates 131 d, 131 d.

[0080] The load added when performing the friction stir welding istransmitted to the surface plate 126 c via two connecting plates 131 d,131 d. Further, the load is transmitted to the other side structure 120via the supporting device 250.

[0081] The embodiment of FIG. 14 will be explained. A supporting device250B mounted on a base 210B is placed between the two side structures120, 120, and the supporting device 250 is mounted thereto. Afterwelding the interior of the car body, the body is supported by thesupporting device 250. The supporting device 250 can be equipped with aroller or a rotary tool, as explained in the former embodiment. When thesupporting device 250 comprises a roller or rotary tool, it moves insynchronism with the rotary tool 80.

[0082] The embodiment of FIG. 15 will now be explained. Two members 10and 20 are butted together as mentioned, and arc-welding is performedalong the joint line. The welding is performed continuously along thejoint line. Especially, the areas having a gap is welded so as to fillthe gap as much as possible (FIG. 15(A), (B)).

[0083] Next, friction stir welding is performed using the rotary tool80. In this case, the nugget B being lifted is used instead of theprotrusions 12 and 22. That is, the lower end of the large-diameterportion 81 of the rotary tool 80 is positioned within the lifted nuggetB when performing the friction stir welding. Further, the members 10 and20 can also be provided with protrusions 12 and 22 for welding (FIG.15(C), (D)).

[0084] The welding is performed to fill the gap with filling material.Essentially, the members are butted together so as not to form any gap,so the butted portion forms an I-type beveling. Therefore, there may notbe any nugget (filling material) existing at the lower area of the gap.However, the formed (lifted) nugget B or protrusions 12 and 22 willfunction as the filling material. The strength of the weld should be ata level preventing the nugget B that is not yet friction-stir-weldedfrom parting by the force of the friction stir welding.

[0085] By butting together two members, cutting the same, then movingthe members so as to minimize or rid the groove between the two members,they are ready for friction stir welding.

[0086] The technical scope of the present invention is not limited tothe terms used in the claims or in the summary of the present invention,but is extended to the range in which a person skilled in the art couldeasily substitute based on the present disclosure.

[0087] The present invention provides a good weld by placing a fillingmaterial in the gap formed to the butted area between two members beforeperforming friction stir welding thereto.

[0088] Further, a good weld is achieved by cutting the butted portionbetween two members and moving the two members closer before performingfriction stir welding thereto.

[0089] The friction stir welding between the underframe of the car bodyand the side structures is performed either by using the surface plateof the underframe as supporting means or by placing a supporting devicebetween the two side structures, which facilitates the welding process.

[0090] The friction stir welding between the side structures and theroof structure is performed while arranging a supporting device betweenthe two side structures, which facilitates the welding process.

What is claimed is:
 1. A friction stir welding method, comprising:butting two members together, a gap being formed therebetween; weldingareas of the gap formed at the butted portion where the gap exceeds afirst size; and performing friction stir welding along the joint lineincluding the areas welded.
 2. A friction stir welding method accordingto claim 1, wherein said welding is performed to all the joint lines towhich said friction stir welding is to be performed.
 3. A friction stirwelding method according to claim 2, wherein: a rotary tool used forsaid friction stir welding comprises a smaller diameter portion to beinserted to the welding area, and a larger diameter portion, than thesmaller diameter portion, to be positioned outside the welding area, aboundary being provided between the smaller and larger diameterportions; and said friction stir welding is performed with the boundarybetween said smaller diameter portion and said larger diameter portionbeing positioned within a nugget protruding from surfaces of saidmembers formed during said welding step.
 4. A method for manufacturing acar body, comprising: welding the areas of a gap exceeding a first valueformed at a butted portion between an underframe and side structures orthe butted portion between the side structures and a roof structure; andperforming friction stir welding along the joint line including theareas welded.